All experimental procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of Allen Institute for Brain Science in accordance with NIH guidelines. All characterization was done using adult mice around ages P56 or older. The mice that were characterized were in a mixed genetic background, containing 50–75% C57BL/6 background and the remainders of 129 or other backgrounds from the various Cre lines. For systematic characterization of fluorescent proteins either by their native fluorescence or IHC, perfused brains were cryosectioned using a tape transfer technique, sections were then DAPI stained directly or following antibody staining, and images were captured using automated fluorescent microscopy. Microtome sections of 100-μm thickness from perfused brains were used for confocal imaging of fluorescently labeled cells. For systematic characterization of gene expression by colorimetric ISH or DFISH, the Allen Institute established pipelines for tissue processing, probe hybridization, image capture and data processing were utilized. Informatics signal identification, mapping, and quantification used the Allen Mouse Brain Atlas spatial mapping platform24 (link), 29 . In this pipeline, image series are preprocessed (white-balanced and cropped), then registered to a three-dimensional informatics reference atlas of the C57BL/6J mouse brain28 . This registration enables data to be displayed in 2D sections or reconstructed 3D volumes.